The present invention relates to integrated optical devices. More specifically, the present invention relates to a process for making such devices and devices made by the process.
Various integrated optical devices have been made using various materials including substrates of lithium niobate (LiNbO3). Such devices are made to perform optical (including electro-optical) functions in materials having optical properties.
Typically, the substrate of such an integrated optical device has a layer of silicon dioxide on it and a metal film electrode on the silicon dioxide. However, there are often difficulties in manufacturing with a metal film electrode unless the metal film is thicker than otherwise preferable. The width (i.e., a dimension parallel to the plane of a surface to which the metal film is deposited) of such an electrode is often quite small. If the height or thickness of such a film is greater than the width, avoiding manufacturing artifacts from thickness variations is difficult or impossible. At the same time, the silicon dioxide makes it advisable to use metal film of a minimum thickness. If the width is increased to avoid the artifacts associated with a height greater than width, other manufacturing problems arise. Complicating the matter, the silicon dioxide makes it advisable to use metal film of a minimum thickness such that the artifacts are more likely to occur.
Fluoropolymer coatings such as those sold under the TEFLON trademark of DUPONT have been applied for measuring electrical properties, but do not have proper adhesion properties to be used for optical or microwave frequency applications. The addition of fluorinated surfactants to photoresist solutions to apply a thin film of photoresist to a fluoropolymer surface is described in, for example, U.S. Pat. No. 5,403,437 Beratan et al. entitled Fluorosurfactant in Photoresist for Amorphous Teflon(trademark) Patterning. This patent also describes the use of reactive plasma etching for xe2x80x9cadhesion properties . . . better than as-deposited . . . films.xe2x80x9d The adhesion induced by the reactive ion etching alone is not sufficient to pass an industry-standard tape pull test.
U.S. Pat. No. 5,413,687 issued to Barton et al. and entitled Method for Metalizing Fluoropolymer Substrates describes the use of reactive plasma etching and bias sputtering to apply metal to fluoropolymers.
Accordingly, it is a primary object of the present invention to provide a new and improved process for making integrated optical devices.
Another object of the present invention is to provide a new and improved integrated optical device.
A more specific object of the present invention is to provide integrated optical devices that are less subject to manufacturing artifacts than typical in the past.
A further object of the present invention is to provide integrated optical devices that have advantageous optical, electrical, thermal and/or stress-resistance characteristics.
Yet another object of the present invention is to provide an integrated optical device which is relatively easy to manufacture.
A further object of the present invention is to provide an integrated optical device having a metal film electrode thereon providing advantageous characteristics.
The above and other features of the present invention which will be more readily understood when the following detailed description is considered in conjunction with the accompanying drawing are realized by a method of making an integrated optical device including the steps of, in order: providing a substrate; applying a fluoropolymer solution to coat at least part of the substrate; and creating an electrode by applying a metal film to the fluoropolymer coat.
Preferably, the process further includes the step of, prior to the creating of the electrode, heating the substrate with the fluoropolymer coating on it such that the fluoropolymer coating is annealed, the annealing of the fluoropolymer coating improving the adhesion of the metal film to the fluoropolymer coating. The heating of the substrate with the fluoropolymer coating on it is performed at 60 to 350 degrees centigrade. (More preferably, the heating is done to 100 to 350 degrees centigrade.) This heating is done by ramping the temperature from ambient to a maximum temperature in the range of 60 to 350 degrees centigrade. Prior to the application of the fluoropolymer coating to the substrate, a primer is applied to the substrate. The primer is a fluoro-silane solution applied to the substrate using a spin coater.
After applying the fluoro-silane solution and before applying the fluoropolymer coating, the substrate is heated to drive off solvent in the primer. As an alternative to heating the substrate with the fluoropolymer coating on it such that the fluoropolymer coating is annealed, the adherence of the metal film to the fluoropolymer coating is improved by further including the step of, simultaneously with the application of the metal film, cooling the substrate with the fluoropolymer coating by contacting a thermal sink with the substrate with the fluoropolymer coating.
The substrate is lithium niobate. The metal film is applied by the substeps of applying an adhesion promoter to the fluoropolymer coating and then applying a contact metal and wherein the integrated optical device is an electro-optical device. After application of the fluoropolymer coating, a post annealing heating of the substrate with fluoropolymer coating and metal film is performed by raising the temperature, preferably by ramping (i.e., meaning temperature is raised as a ramp function, either a continuous ramp function or a stepped ramp function), from ambient to a maximum temperature in the range of 60 to 350 degrees centigrade. More preferably, the maximum temperature for this step is 150 to 350 degrees centigrade.
The present invention may alternately be described as a method of making an integrated optical device including the steps of, in order: providing a substrate of lithium niobate; applying a fluoropolymer solution to coat at least part of the substrate; and preparing the substrate having fluoropolymer coat such that a metal film will adhere to the fluoropolymer coating. Preferably, after the preparing the substrate having fluoropolymer coat, an electrode is created by applying a metal film to the fluoropolymer coat.
The preparing of the substrate having fluoropolymer coating may include heating the substrate with the fluoropolymer coating on it such that the fluoropolymer coating is annealed, the annealing of the fluoropolymer coating improving the adhesion of the metal film to the fluoropolymer coating. The heating of the substrate with the fluoropolymer coating on it is performed by ramping the temperature from ambient to a maximum temperature in the range of 60 to 350 degrees centigrade. Prior to the application of the fluoropolymer coating to the substrate, a primer is applied to the substrate. The primer is a fluoro-silane solution applied to the substrate using a spin coater. (Other coating methods such as spraying and evaporation may be used as well.) After applying the fluoro-silane solution and before applying the fluoropolymer coating, the substrate is heated to drive off solvent in the primer.
An alternate preparing of the substrate having fluoropolymer coating includes, simultaneously with the application of the metal film, cooling the substrate with the fluoropolymer coating by contacting a thermal sink with the substrate with the fluoropolymer coating.
The metal film is applied by the substeps of applying an adhesion promoter to the fluoropolymer coating and then applying a contact metal. A post annealing heating of the substrate with fluoropolymer coating and metal film is performed by ramping at a controlled rate (1-10xc2x0 C./min) the temperature from ambient to a maximum temperature in the range of 60 to 350 degrees centigrade.
The present invention may alternately be described as an integrated optical device including: a substrate; a fluoropolymer coat on the substrate; and a metal film electrode on the fluoropolymer coat. The substrate is lithium niobate. The metal film is from 0.1 to 20 xcexcm thick. The metal film includes an adhesion-promoter layer of from 100 to 1000 Angstroms. The integrated optical device is an electro-optical device.